The B. subtilis sigma-B protein is involved in activation of transcription of a stress response regulon. In the absence of environmental stress, sigma-B is held in an inactive complex with an anti-sigma (RsbW). Unknown stress signals cause a second regulatory protein, RsbT, to phosphorylate and inactivate its own inhibitor, RsbS. Active RsbT directs a phosphatase, RsbU, to dephosphorylate another regulator, RsbV. Dephosphorylated RsbV can then bind to RsbW, causing release from sigma-B, allowing the sigma to be active as a transcription factor. The system is reset by a second phosphatase, RsbX, which dephosphorylates and reactivates RsbS, so that it can again inhibit RsbT. Inhibition of RsbT results in phosphorylation of RsbV, preventing interaction with RsbW, so that RsbW is once again available to trap sigma-B in an inactive complex. The proposal seeks to determine how diverse stresses can communicate with the regulators of sigma-B to control its activity. High sigma-B activity, resulting from loss of RsbX, is toxic to the cell; this permits isolation of suppressor mutations, and identification of genes involved in this pathway. RsbT and RsbX are postulated to be the most likely direct targets of environmental signals; this will be tested by detailed mutational analysis. Biochemical analyses will be used to monitor in vivo phosphorylation of RbsS, which is proposed to be a key step in the sigma-B activation cascade. Proteins which interact with Rsb proteins will be sought by biochemical analyses and using the yeast dihybrid system. Since sigma-B homologs have been discovered in pathogenic bacteria, analysis of control of the stress response may provide information about adaptation to the host and infectivity.